Communication system



July 28, 1942.

Filed June 6, 1941 /N VEN TOR H. N VQ U/ST A Tron/VE v Patented July 28,1942 g COMMUNICATION SYSTEM Harry Nyquist, Millburn, N. J., assignor tovBell Telephone Laboratories,

Incorporated, New

York, N. Y., a corporation of New YorkI Y Application June 6, 1941, Serial No. 396,839

11 Claims. (Cl. 179-18) This invention relates to communication systems and particularly to a signaling means for use therein.

An object of the invention is to increase the speed of dialing.

Another object isto provide a signaling system in which the distance of the subscribers station has comparatively little impairment upon the character of the pulses received bythe vcentral oflice switching mechanism.

Still another object is to eliminate pulsing contacts at the subscribers station and to provide at the central office a pulse generator that actuates the switching mechanism with pulses more uniform in speed, percentage break, and current strength. v

vA further object is to provide a calling device in which a single impulse is transmitted for each digit dialed, the length of the impulse being proportional to the digit dialed.

Still a further object is to eliminate the customary mechanical governor and spring in a calling device and electrically return the dial to its normal position in synchronism with the operation of a pulse generator at a central oflice.

With the above objects in view, an embodiment of this invention discloses a system in which a simplied dialing unit having an inductor motor return movement is provided at the subscribers station and in'which ,a pulse generator operative in synchronism with said return movement is provided, at the central cnice. The subscribers dialing signal comprises a single impulse, rather than the commonly used variable impulses of equal length, for each actuation of the dial. The duration of this impulse variesV in accordance with the digit dialed, and is of shortest period for the digit 1 and of longest period for the digit O. The duration of dial return, therefore, determines the quantity of pulses generated by the pulse generator, which pulses in turn actuate the switching mechanism in the wellknown manner. Since the pulses are generated in the central oice rather than at the subscribers station, they can be made more nearlyuniform in speed, percentage break, and current strength and moreover, they can be made substantially uniform in shape.

A more complete understanding of this invention will be obtained from the detailed description which follows and by reference to the appended drawing which shows one embodiment thereof.

Referring to the drawing there is shown diagrammatically at one end of a transmission line a telephone subscribers station having a novel inductor motor type of calling device I0 and at the other end of the line, a central oice having a pulse generator PG with associated control apparatus interposed between a line-finder circuit LF or a line switch (not shown), as the case may be, and a selector switch (not shown).

Thecalling `device will be first described. In appearance the calling device is somewhat similar tothe well-'known impulse transmitting devices that are in common use'in automatic tele- 'phone systems but is distinguished in that the governor, impulse cam, and transmitting springs have been omittedtherefrom. In lieu thereof there is provided a special impulse transmitting unit which opens the line circuit once for each actuation of the calling device dial, the duration of the open circuit depending upon the digit in accordance with which the dial is operated.

The calling device I0 comprises a linger-hole dial II with the customary linger stop FS. Rigidly secured to the dial I I by'any suitable means is one end of a tubular member I2 which has mounted thereon at its other end a contact spring I 3, which upon rotation of dial II also rotates therewith. -Spring I3 is equipped at its free end with a contact I4 while intermediate therewith is fastened one end of a spring I5, the other end'of which is insulated by an insulator 9= and secured in a suitable manner to a contact spring I6 having a contact `I'I cooperating with contact I4. Contacts j|4 and I1 are -normally-separated from each other by spring I5 butduring the" clockwise rotation of dial II, the pressure exerted by contact spring I3 upon separative spring I5 'is suiiicient to eifect closure of contacts I4 and I1.Y Upon the return movement of the dial, as explained hereinafter, spring I5 is suiciently strong to again separate contacts I4 and I1 inasmuch as the dial offers very little, if any, frictionall resistance thereto.

Contact spring I6 is fastened to a shaft I8 which is insulatedly journaled at one end in tubular member I 2 and at the other end in a frame (not shown) of the dial unit. Shaft I8 freelyrotates in said journals and intermediate therewith is secured a hub I9 of an inductor 20 by any Asuitable means such as a pin 2|. Hub I9 may be integral to inductor 20 or may comprise a separate element secured thereto. Around a large portion ofthe periphery of inductor 20 are -arranged teeth 22, which, after having been rotated mechanically in a clockwise direction by `therlnger dial, are attracted by a stator 23 energizedby alternating current through a winding the rotors rotation.

24 to cause the inductor 2l) to rotate counterclockwise and return to its normal position. A capacitance 25 of suitable value is inserted in series with winding 24 to prevent flow of direct current and permit flow of alternating current therethrough during the return movement of the dial II. fA cam 26 is also located on the periphery of inductor 20 between the end teeth 22 for actuating a switch 21 when inductor 20 is rotated from its normal position. The remaining apparatus at the subscribers station comprise the usual transmitter, receiver, etc., that are well known in the telephone art.

The pulse generator PG at the central ofce will be described next. The line-nder circuit LF and the switching mechanism (not shown) will not be described as they are not vitally concerned with applicants arrangement although at the same time they comprise elements well known in the switching art.v A

The pulse generator PG comprises a rtor 28 having teeth T of soft iron; Eight teeth are shown on said rotor but applicant does not limit himself to this number of teethas the same speed o f rotation may be obtained by otherquantities of teeth. Rotor 28 is rigidly sered to a shaft 29 and rotates ata speed of 15 revlutiens per second when energized from a (50i-'cycle source. That is, the rotor 28 advances two teeth in accordance with the attraction of first one electromagnet and then the other, as explained hereinafter, and since the rotor comprises eight teeth, it will make one revolution every four cycles. To oneof the teeth T is affixed a pin 30 composed of soft iron orof permanent magnetic material in order to function as a south pole. The pin 39 is positioned in a plane different from that of the rotor teeth T. l

Cooperating with the rotor 28 uare electromagnets 3l and 32 having windings 33 and 3 4, respectively, thereon. Both windings areY connectedin parallel, winding 33 also being serially connected with an inductance 35 and winding 34 serially connected with a capacitance 36. `Because of the incluctance 35 and capacitance 36, the electromagnets 3|V and 32 alternately energize 'a't a phase vdisplacement of 90 degreesrst one electromagnet being energizedfand then theuotherr. This alternate*energization of the electromagnets attracts rotor 28 in such manner as to cause its rotation in either direction at a speed dependent upon the frequency applied to 'the electromagnet. Onev embodiment which is disclosed herein, Yemploys a sinusoidal frequency of 60 cycles.

After the pulsing operation has ceased, it is desirable to return the'r'otor 28 Ato its'normal position. Applicant accomplishes vthis by locating a permanent magnet 31 in the same plane 'as that 'of pin at, with the nrthjpole N ormegnet 31 opposite the V'south pole of pin, 30. Uponde'- energization of electromagnets 3| and 32, rotor 28 is released and pin 3D being attached thereto is 'attracted by magnet 31 to return the rotr 2 8 to its normal position.. For thispurpos'e magnet 31 is sufciently strong toadetermine the rest position of the rotor 28, but at the same time weak enough vnot to interfere lapp'reciably with A cam 38 is `also rigidlysec'ured to `shaft '29, which likewise makes one revolution'everyjour cycles. Cam 38 cooperates with an armature 39 and insulated arin 4I! of a switch S to open :nor-

'many closed Contact 4l thereof, The cotquf vof the cam 38 is s'o shaped as to break the switch contact 4I sixty per cent of the time during each revolution of the cam; and thus provides optimum percentage break. In other words, during each revolution of the rotor 28, a break of 60 per cent duration occurs in the switching mechanism circuit. A restraining spring 42 effects intimate contact of armature 39 over the periphery of cam 38.

` The control relays associated with the pulse generator at the central oii'ce are the ordinary telephone type relays of well-known construction. The functions of these relays will be explained lfully during the description of the circuit operation. In addition to the control relays, condensers CI and C2 and inductances LI and L2 may be interposedvin the talking path to separate the signaling from the Voice channel. Resistance R may be inserted in the switching mechanism circuit to give the signal current generated by the pulse generator PG optimum value, while condenser C in parallel with resistance R may be added to reduce the transmission loss caused by resistance R if inductances LI and L2 are small.

The operationof the dialing system will now be described. Upon removal of the receiver 43 from the switclihook 44, in order to initiate a call at a subscribers station, a circuit is closed through the usual line relay (not shbwn) located at the central cnice. Closure of the line relay initiates the operation of a line iinder in a manner that is well known. When the line-finder circuit LF is operated, a circuit is closed from the negative pole of battery 45, at the central oflice, through the upper winding of relay 46, conductor 41, line-iinder circuit LF, and thence over conductor 48 ofthe transmission line through coil 49, over'conductors 50 and 5 I ,through transmitter 52, conductor 53, lower break contact 'of 4switch 21, conductor 54, lower make 'contact 'of swltchhook 44, and back to the central vo'i-Iice over con'd'uctor 55, through line-iinder circuit LF, conductor 56, and Vthence through lower winding "of relay 46 to positive pole of battery 45. Relay 46 energizes and immediately thereafter relay y51 oper- 4ates in a circuit (not shown) to close its front contact and prepares a 'circuit for supplying alternating current both to the subscribers line and to the pulse generator. The front contact of relay 51 is interposed in this circuit primarily to eliminate the `continuous and. wasteful -opera-- tion of the pulse generator PG duringidl'e periods and may be made a part of the well-known cut-off relay of the line circuit (not shown), which relay operates `after the line Vfinder has seized 'the calling lin'e. Applicant, however, does not Vlimit himself to the use 'of such relay as other means known to one versed in the art are available. Relay 46 nbperating closes at its bottom front contact the pulsing 'circuit tothe switching mechanism (not shown) and prevents at its upper contacts the application 'of alternating current to the calling device/and vpulse generator.

Meanwhile the usual tone signal is transmitted to the subscriber informing him that the central office switching mechanism is 'ready to receive his dial impulses. The calling subscriber "now inserts his fing-er intovone 'of Athe lingerr holes '53 and moves dial I'I clockwise until thenger lstop FS has been reached. At the beginning fof rotation Of dial I I, contacts I4 and `|`I "engage after overcoming the resistance of spring I5 and shunt lthe Ylower break contact f A,svi/itch '121 over conductors 59 yandim, which are conneeted directly to'springs I3 and I6, respectively. Applicant, however, doesl not limit himself to this connecting means as other well-known means such asl the slip ring and brush construction may be substituted therefor. In addition, the pressure of contact I4 upon contact I1 forces shaft I8, and in turn vrotor 26, to rotate clockwise (in the direction of the arrow) with the dial. As rotor 26 moves clockwise, cam 26 disengages itself from switch 21 and opens the lower contact thereof. However, this has no eiTect asrthe closure of contacts I4 and I1 had already created a parallel operating circuit for relay 46. When the nger stop FS is reached, and the finger is withdrawn, contacts I4 and I1 are separated by the force of spring I5 thereby d-eenergizing relay 46. At the same time dial II starts back in 4a manner to be hereinafter described. H

TheVv release of relay 46 causes (iO-cycle energy to be applied to the subscribers line to inductively return dial I I to its normal position. This circuit may be traced from the upper terminal of the 60-cycle source 6I through upper winding of relayv62, capacitance 63, conductor 64, lowermost upper back contact of relay 46, conductor 41, thence through line-lnder circuit LF, over conductor 48, through coil 49, conductor 50, upper front contact of switchhook 44, conductor '65, upper front contact of switch 21, conductors 66,

53, and 68, through winding 24, capacitance 25,

conductors 69 Yand 54, through lower make contact of switchhook 44, and back ov-er conductor 55 through line-nder circuit LF, conductors 56 and 10, back contact of relay 46, conductor 1I, capacitance 12, through lower winding of relay 62, conductor 13, and thence through front contact of relay 51 to bottom terminal of source 6I. Relay 62 energizes over the above-traced circuit and closes the front contact thereof to maintain the pulsing circuit (as trac-ed hereinafter) in a closed condition. The release of the bottom front contact of relay 46 is therefore retarded to permit prior energization of relay 62.

Stator magnet 23 isalternately energized and deenergized by the sinusoidal current from source 6I and attracts teeth 22 in a manner well known in the art to cause the rotor 20, and in turn,

dial Il to rotate counter-clockwise back to its normal position. The teeth 22 of rotor 20 may be of soft iron or may be so constructed that alternate ones are north and south poles. Furthermore, the teeth are so spaced that the speed of return is held accurately to a speed corresponding to fifteen pulses per second. After a time interval corresponding in length to the digit dialed, cam 26 closes the lower contact of switch 21, which energizes relay 46 in a circuit -already traced. The operation of relay 46 disconnects 60- cycle source -6I and thereby releases relay 62. The interval during which 60-cycle energy is applied to the subscribers line is one-fifteenth of a second if the digit 1 is dialed, tWo-lfteenths of a second if the digit 2 is dialed, and progressively to ten-lifteenths of a second when the digit 0 is dialed.

While the Gil-cycle energy is applied to the line, it also is applied simultaneously to the pulse generator PG to cause the latter to likewise operate synchronously with the return movement of the calling dial II. The circuit for energizing the pulse generator PG may be trac-ed from the upper terminal of the (S0-cycle source 6 I, over conductor 14, through uppermost back contact of relay 46, and thence in parallel paths, one path through winding 33 of electromagnet 3l and inductance 35, and the other path through winding 34 of electromagnet 32 and capacitance 36, thence through upper back Contact of relay 46, conductor 13, andthrough front contact of relay 51 to bottom termin-al of source 6 I. As previously described, the electromagnets 3| and 32 are alternately energized and as a result cause therotor 28`and cam 38 to rotate synchronously with the return movement of the dial II 'at a rate of fifteen revolutions per second. This synchronous rotation of rotor 28 of the pulse generator PG in turn opens the switching mechanism circuit at contact 4I once for each revolution, in a manner already described. This circuit may be traced fromv inductance LI through back contact 4I of switch S, resistance R, over conductor 15, front contact of relay 62, over conductor'16, through inductance L2, and thence through loop of selector switch (not shown) back through inductance LI. Upon rotation of cam 38, the armature 39 with its insulated arm 40 is raised and lowered in such manner as to cause the back contact 4I of switch S to alternately break and make the above-traced circuit, which in turn steps the magnets (not shown) of the switching mechanism in the well-known manner. After the dial II returns to its normal position, relay 46 operates, as previously described, and disconnects the 60-cycle source 6I from windings 32 and 33 whereupon the pulse generator returns to its normal position in a manner already described.

When the subscriber dials the second digit, the above operations are repeated. This procedure continues until the proper number of digits have been dialed and the desired selection has been e'ected.

The connection is released. in the usual manner by restoring receiver 43 to its switchhook 44 whereupon the subscribers line cir-cuit is opened lto release line finder LF' and relays 46 and 51.

Relay 46 in releasingr opens the switching mechanism circuit at the lower front contact thereof while relay 51 at its front contact disconnects source 6I. The circuit is now in readiness for anothercall.

While the features of this invention have been disclosed with reference to a specific embodiment only, it is, of course, understood that Various modifications may be made in the details of construction without departing from the scope of this invention as defined in the appended claims.

What is claimed is:

1. A signaling system comprising a reciprocating dial movable in accordance with diierent digital values and alternating current responsive means for restoring said dial to its normal position.

2.` In a signaling system, a reciprocating dial movable in accordance with different digital values and inductor motor means for returning said dial to its normal position.

3. In a signaling system, a reciprocating dial movable in accordance with different digital values, an inductor motor for restoring said dial to its normal position, a source of alternating current for driving said motor, and impulse means driven by said source synchronously with said motor.

4. In a signaling system, a subscribers substation, a reciprocating dial in said substation movable in accordance With different digital values, an electroresponsive device for returning said dial to its normal position, a source of alternating current at a telephone central oice for driving said device, a line circuit extending between said substation and said central omce, and impulse means at said central office driven by said source concurrently with said device.

5. A signaling system comprising a dial movable from its normal position in accordance with different digital values, an alternating current motor for returning said dial to its normal position, a source of alternating current for driving the motor, and a pulse generator driven by said source synchronously with said motor for producing impulses proportional in duration to the digit dialed.

6. In a signaling system, a calling device having a reciprocating dial, electroresponsive means for regulating the return movement of the dial at a predetermined speed after each setting thereof, a line circuit, a source of alternating current for actuating said electroresponsive means, and an electroresponsive device driven by said source synchronously with said means.

'7. In a signaling system, a calling device having a reciprocating dial, a motor, a rotor and stator in said motor, a coupling connecting the dial with the rotor, a switch on said coupling, said switch being closed during the forward movement and opened during the return movement of said dial, and a Winding on said stator in series with a condenser connected in parallel relationship with said switch, said condenser providing a closed circuit to alternating current and an open circuit to direct current during the return movement of the dial.

8. In a signaling system, a subscribers station, a calling device at said station having a reciprocal dial, means in said device for transmitting a single impulse at each actuation of the dial, the durtion of said impulse being proportional to .the digit dialed, an impulse generator at a telephone central office, and means including a line circuit extending between said calling device and said generator for driving said impulse generator an interval of time proportional to the `duration of said impulse.

9. In a signaling system, a calling device having a reciprocating dial, normally closed springs and normally opened springs connected in parallel relationship, a capacitance and inductance connected in parallel with said springs, a source of direct current and of alternating current, means for maintaining said normally closed springs in an open condition and said normally open springs in a closed condition during the actuation of said dial to a nger stop thereof, thereby providing a closed circuit for direct current, means for opening said normally open springs during the return movement of said dial whereby said circuit is opened to direct current, and means responsive to said open circuit for connecting said alternating current source to said capacitance and inductance during the return movement of said dial.

10. In a signaling system, a calling device having a reciprocating dial, an electroresponsive pulse generator, a line circuit extending between said calling device and generator, means included in said calling device for opening the line circuit for a duration of time proportional to the digit dialed, means controlled over said line circuit responsive to the opening thereof for operating said pulse generator for the duration of said open circuit, and means for restoring said pulse generator to its normal position upon closure of said line circuit.

11. In a signaling system, a calling device having a reciprocating dial, an electroresponsive pulse generator, a line circuit extending between the Vcalling device and generator, a source of direct current and alternating current, switch means included in said calling device for opening the line circuit to direct current and closing it to alternating current for a period of time proportional to the digit dialed, means controlled over said line circuit responsive to the opening thereof for operating said pulse generator for the duration of said open circuit, switch means periodically opened and closed during the operation of said pulse generator, and means for restoring said pulse generator to its normal position upon closure of said line circuit.

HARRY NYQUIST. 

